1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a transflective liquid crystal display device selectively using reflective and transmissive modes, and a fabricating method thereof.
2. Discussion of the Related Art
Generally, transflective liquid crystal display (LCD) devices function as both transmissive and reflective LCD devices at the same time. Because the transflective LCD devices can use both the light from a backlight, and exterior natural or artificial light, transflective LCD devices may be used in more circumstances and the power consumption of the transflective LCD devices may be reduced.
FIG. 1 is a schematic cross-sectional view of an array substrate for a transflective liquid crystal display device according to the related art. A gate line 52 and a data line 62 are formed on a substrate 50. The gate line 52 and the data line 62 cross each other to define a pixel region “P.” A thin film transistor (TFT) “T” including a gate electrode 54, an active layer 56, and source and drain electrodes 58 and 60 are disposed the intersection of the gate line 52 and the data line 62. The pixel region “P” includes a reflective portion “C” and a transmissive portion “D.” A reflective electrode 64 and a transparent electrode 66 correspond to the reflective portion “C” and the transmissive portion “D,” respectively. An island shaped metal pattern 63 overlaps a portion of the gate line 52 and contacts the reflective electrode 64 or the transparent electrode 66. The metal pattern 63 and the overlapped portion of the gate line 52 constitute a storage capacitor “CST.”
FIGS. 2 and 3 are schematic cross-sectional views of a transflective liquid crystal display device according to first and second embodiments of the related art. FIGS. 2 and 3 are taken along a line “II—II” of FIG. 1. First and second substrates 50 and 80 face each other and are spaced apart from each other. The first and second substrates 50 and 80 include a plurality of pixel regions “P.” A gate line (not shown) and a data 62 line crossing each other are formed on an inner surface of the first substrate 50. Red, green and blue (not shown) sub-color filters 84a and 84b are formed on an inner surface of the second substrate 80, and a black matrix 82 is disposed between the sub-color filters 84a and 84b. A transparent common electrode 86 is formed on the sub-color filters 84a and 84b, and the black matrix 82. The pixel region “P” includes a reflective portion “C” and a transmissive portion “D.” Generally, a reflective electrode 64 corresponding to the reflective portion “C” and a transparent electrode 66 corresponding to the transmissive portion “D” are formed over an inner surface of the first substrate 50. The reflective electrode 64 having a transmissive hole “H” can be formed over or under the transparent electrode 66.
Reducing the color difference between the reflective and transmissive portions “C” and “D” is very important in the transflective LCD device. In FIG. 2, because the light path (the distance that the light travels when light passes through the liquid crystal layer) in the reflective portion “C” is different from that in the transmissive portion “D,” the polarization properties in the reflective and transmissive portions “C” and “D” are also different from each other. In the transmissive portion “D”, the light passes through a liquid crystal layer 90 having a thickness “d.” In the reflective portion “C,” light passes through the liquid crystal layer 90, is reflected at the reflective electrode 64, and then passes through the liquid crystal layer 90 again. Accordingly, the light path in the reflective portion “C” is twice the length of that in the transmissive portion “D.” Thus, the light has different polarization properties in the reflective and transmissive portions “C” and “D,” thereby a difference in color purity may occur.
To solve this problem, as shown in FIG. 3, an insulating layer 63 in the transmissive portion “D” has an open portion 61 so that the light path in the reflective portion “C” can be the same as that in the transmissive portion “D.” When the liquid crystal layer 90 in the reflective portion “C” has a thickness of “d,” the liquid crystal layer 90 in the transmissive portion “D” has a thickness of “2d,” i.e., the liquid crystal layer 90 has a dual cell gap.
However, even though light efficiency of the reflective portion “C” is the same as that of the transmissive portion “D” due to the dual cell gap, uniform color purity cannot be obtained. The sub-color filter “R” in the reflective portion “C” has the same thickness as that in the transmissive portion “D.” Light passes through the sub-color filter “R” twice in the reflective portion “C,” while light passes through the sub-color filter “R” just once in the transmissive portion “D.” Accordingly, even though a light source for the transmissive mode is brighter than that for a reflective mode, light emitted from the reflective portion “C” has higher color purity than that emitted from the transmissive portion “D.” To solve this problem, a method is suggested wherein the sub-color filter corresponding to the reflective portion has a hole.
FIG. 4 is a schematic plane view showing a sub-color filter for a transflective liquid crystal display device according to a third embodiment of the related art. A sub-color filter 84 corresponds to reflective and transmissive portions “C” and “D.” The sub-color filter 84 corresponding to the reflective portion “C” has a hole 88 filled with organic material (not shown). Because the hole 88 transmits light in the reflective portion “C,” the hole 88 reduces absorption of light in the whole sub-color filter 84.
FIGS. 5A to 5C are schematic cross-sectional views showing a fabricating method of a sub-color filter for a transflective liquid crystal display device according to the third embodiment of the related art. FIGS. 5A to 5C are taken along a line “V—V” of FIG. 4.
In FIG. 5A, a sub-color filter 84 is formed on a substrate 80 by coating a color resin. In FIG. 5B, a hole 88 is formed in the sub-color filter 84 corresponding to a reflective portion “C” by patterning. In FIG. 5C, an overcoat layer 90 is formed on the sub-color filter 84 by depositing a transparent organic material. A transparent common electrode 92 is formed on the overcoat layer 90.
In the above structure, however, light passing through the hole 88 has a poor wavelength filtering effect so that color purity of the whole sub-color filter 84 is reduced. Moreover, because the hole 88 has a diameter over about 10 μm due to the color resin property, the average effect between the light passing the hole 88 and the sub-color filter 84 is reduced.
To solve this problem, a method decreasing the color difference between the reflective and transmissive portions by forming a transparent buffer layer under the sub-color filter in the reflective portion is suggested. In this method, because the thickness of the sub-color filter in the transmissive portion is twice of that in the reflective portion, the color difference between the reflective and transmissive portions is reduced.
FIG. 6 is a schematic cross-sectional view of a transflective liquid crystal display device according to a fourth embodiment of the related art. FIG. 6 is taken along a line “II—II” of FIG. 1. The first and second substrates 50 and 80 having a pixel region “P” face each other and are spaced apart from each other, and a liquid crystal layer 90 is interposed therebetween. A black matrix 82 and red and green sub-color filters 84a and 84b are formed on an inner surface of the second substrate 80. A common electrode 86 is formed on the red and green sub-color filters 84a and 84b. Even though not shown in FIG. 6, a planarization layer can be formed between the common electrode 86 and the sub-color filters 84a and 84b. 
The pixel region “P” includes a reflective portion “C” and a transmissive portion “D.” A reflective electrode 64 and a transparent electrode 66 correspond to the reflective and transmissive portions “C” and “D,” respectively. Generally, the reflective electrode 64 having a hole “H” is formed under the transparent electrode 66. Because an insulating layer 63 under the reflective electrode 64 has an open portion corresponding to the hole “H,” the liquid crystal layer 90 in the transmissive portion “D” has a thickness of “2d” when the liquid crystal layer 90 in the reflective portion “C has a thickness of “d,” i.e., the thickness of the liquid crystal layer 90 in the transmissive portion “D” is substantially twice of that in the reflective portion “C.”
A buffer layer 83 corresponding to the reflective portion “C” is formed between the second substrate 80 and the sub-color filters 84a and 84b. The color resin flows to form the sub-color filters 84a and 84b. Accordingly, the sub-color filters 84a and 84b in the transmissive portion “D” has a thickness of “2t,” while the sub-color filters 84a and 84b in the reflective portion “C” has a thickness of “t.”
However, because the buffer layer is formed in the reflective portion, the fabricating process of the buffer layer is not simple and a production yield is reduced. Especially, when the reflective and transmissive portions are disposed as in FIG. 1, the reflective electrode is elongated along a direction parallel to the data line. Accordingly, the reflection efficiency is reduced in the right and left views.